(Combination) In mathematics, a combination is a selection of items from a collection, such that (unlike permutations) the order of selection does not matter. If the set has n elements, the number of k-combinations is equal to the binomial coefficient.

Given two integers n and k, return the number of all possible combinations of k numbers out of n elements.

The input consists of m (0<m<100) lines.
Each line consists of n (ranges from 1 to 10), k (ranges from 1 to n).
The last line of input consists of Int(-1).

Output the number of all possible combinations of k numbers out of n elements.